Proposal : Use bump memory context for temp buffers

Hi,

Commit [1] introduced a new memory context suitable for situations when we
should allocate a large amount of memory with no need to free or reallocate it.

I think that it will be useful for temp buffers :
1) We allocate them lazily and never try to free them.
2) Some users are very active in working with temporary tables, and as
a result,
they set large values for the "temp_buffers" parameter (several gigabytes).

Thus, the use case for temp buffers seems to perfectly fit for bump
memory context.
What do you think?

[1] 29f6a959cfd8ffa7d6db2c0629439c5329e2853e

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Best regards,
Daniil Davydov